The invention concerns a device and a method for detecting nonlinear electronic components or electronic circuits, especially for detecting the electronics of an improvised explosive device (IED).
A well-known method for detecting nonlinear components is nonlinear junction detection (NLJD). This method has the ability to detect electronic circuits built with semiconductor components. As a result of the nonlinear behavior, signals of a fixed frequency coupled into the circuit are converted to signals with a multiple of the emitted frequency and are reemitted. A method of this type and a corresponding nonlinear junction detector are described in detail in U.S. Pat. No. 6,163,259 A. Another nonlinear junction detector is disclosed by WO 02/065419 A1. Another patent, WO 2004/038455 A1, concerns a method and a device for detecting eavesdropping devices. In principle, the method works by evaluating a second and a third harmonic primary frequency reflected at the target. Information about the presence or absence of an electronic circuit is then derived from these two harmonics.
IED's are devices or explosive booby traps that usually consist of four major groups of components: a trigger, explosives, alone or combined with poisonous chemicals, toxic biological materials or radiological material, and an effector. The trigger can be mechanical or electronic in nature.
To avoid danger, it is necessary to know whether an IED is present, where it is located, when a detonation of this IED is to be feared, and how much and what type of explosive it contains. Other information it would be important to know is whether biological or radioactive materials are present in the IED. In this connection, the explosive can be detected, for example, by known laser technologies or x-rays, and information about the biological content can be obtained, for example, by the use of biosensors. If the IED's additionally contain an electronic system, e.g., an electronic ignition circuit, a search can also be made for the presence of these electronics, for example, by means of the aforementioned NLJD.
The detection range of a target (for example, an IED) depends to a great extent on the signal-to-noise ratio of the harmonic frequencies. In practical investigations, it was determined that there is a difference in detection distance by a factor of almost 8 to 12 between simple circuits and circuits with high-grade shielding. This corresponds to a factor of 4,000-20,000 for the received signal lines.
Due to the signal-to-noise ratio of the amplifier connected on the load side and possible modulation processes, there is a minimum received power at the receiver that is necessary for detection.
With respect to the transmitting power, there are both CW systems (continuous-wave systems) and pulsed systems for manual operation. However, where manual operation is concerned, the transmitting power is limited by values based on personal protection criteria.